Photographic products, processes and compositions



June 21, 1966 Filed Aug. 30, 1963 M. GREEN 3,257,207

PHOTOGRAPHIO PRODUCTS, PROCESSES AND COMPOSITIONS .2 Sheets-Swat 1 SUPPORT PHOTOSENSITIVE LAYER COMPOSITION 1 IMAGE-RECEIVING LAYER SUPPORT SPREADER SHEET SSING COMPOSITION PHOTOSENSITIVE LAYER IMAGE-RECEIVING LAYER SUPPORT INVENTOR.

BY M

WW- M ATTORNEYS June 21, 1966 REFLECTION DENSITY Filed Aug. 30, 1965 M. GREEN 3,257,207

PHOTOGRAPHIC PRODUCTS, PROCESSES AND COMPOSITIONS 2 Sheets-Sheet 2 0.5- 0.4- o5 METER-CANDLE-SECONDS 02" 00010 .00080 .0O\6\ 0032 QO64 013 :025---.... 00013 00025 00050 .0010 0020 0040 .0080 .016 .032 "00060 .00016 00032 ,00 .0013 i .010 .020 .040 1 111111 1 REFLECTION 0.80 DENSITY 050 0.40

l l I I l l 012345618910 INVENTOR.

BY MAWMM M WW k4- AII'TORNEYS United States Patent 0 3,257,207 PHOTOGRAPHIC PRODUCTS, PROCESSES AND COMPOSITIONS Milton Green, Newton, Mass, assignor to Polaroid Corporation, Cambridge, Mass, a corporation of Delaware Filed Aug. 30, 1963, Ser. No. 305,781 12 Claims. (Cl. 96-29) emulsion is developed. Almost concurrently therewith,-

a soluble silver complex is obtained by reaction of a silver halide solvent with the unexposed and undeveloped silver halide of said emulsion- Preferably, the photosensitive silver halide emulsion is developed with a processing composition in a viscous condition, which is spread between the photosensitive elementcomprising the silver halide emulsion and a print-receiving element comp-rising, preferably, a suitable silver precipitating layer. The processing composition effects development of the latent image in the emulsion and substantially contemporaneous therewith forms asoluble silver complex, for example,

' a thiosulfate or thiocyanate complex, with undeveloped silver halide. This soluble silver complex is, at least in part, transported in the direction of the print-receiving element and the silver thereof is largely precipitated in the silver precipitating layer of said element to form 'the desired positive image therein.

High speed diffusion transfer processes of the present invention are generally of the type in which, for example, a silver halide stratum containing a latent image formed at a low exposure level and an image-receiving stratum, in superposition, are subjected to a processing composition containing a highly energetic silver halide developing agent set forth hereinafter and a silver halide solvent in order to form a silver transfer print in and/or on the image-receiving stratum. The silver halide developing agent serves to reduce photoexposed silver halide to silver in the photosensitive emulsion stratum. The silver halide solvent reacts with unreduced silver halide to form the aforementioned soluble silver complex which, in turn, is reduced in the presence of the image receivin g stratum to form the desired positive print. The photosensitive stratum may be subsequently dissociated from the imagereceiving stratum. In accordance with the present invention, the silver halide stratum may be underexposed in relation to its rated A.S.A. Exposure Index and the silver halide developing agent is specifically selected from the class hereinafter set forth in order to provide the results detailed. Preferably, the image-receiving stratum 'employed is in such conditionas to cause silver reduced there, in comparison with silver reduced in the photosensitive silver halide stratum, to possess very high covering power, that is, opacity per given mass of reduced silver. This high covering power is achieved by accumulating the "ice silver deposited in the silver-receptive stratum in unusually dense masses, for example, by minimizing the thickness of the stratum in vvhich the silver-receptive material is contained.

High speed diffusion transfer processes according to the procedure set forth herein, in addition to their relativeiy high speed, possess an extensive dynamic range and thus provide a readily available and uniquely simple process for producing high quality prints of good resolution and trivial granularity over an extensive range of exposure, commencing at low illumination levels, for example, at overall exposures that are equivalent to A.S.A. Exposure Indices of 1,000 and up.

Accordingly, objects of the present invention are to provide novel compositions, products and photographic processes and, in particular, photographic high speed diffusion transfer processes possessing an extended dynamic range, wherein a selectively photoexposed silver halide emulsion may be substantially underexposed in relation to its A.S.A. Exposure Index, to provide high quality, full scale transfer image formation; and to employ, in compositions, products and processes of the aforementioned type, as a silver halide developing agent, 2,3,6-t-rirnethyl-p-aminophenol and/or 2,3,5-trimethyl-p-anrinophenol.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the products and compositions possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic enlarged cross-sectional view illustrating the association of elements during one stage of the performance of a diffusion transfer process, for the production of positive silver prints, the thickness of the various materials being exaggerated;

BIG. 2 is a view similar to that of FIGURE 1 illustrating the association of elements during one stage of the performance of another diffusion transfer process, for the production of positive silver prints;

FIG. 3 is a graph showing characteristic curves of silver transfer images determined by plotting the reflection density of the transfer image as a function of the log exposure of the photoresponsive silver halide emulsion, wherein Curves A and B represent the characteristic curves of transfer images prepared in accordance with the present invention and employing 2,3,6-trimethyl-paminophenol and '2,3,5-trimethyl-paminophenol, respectively, as the silver halide developing agent, and Curves C and D represent the characteristic curves of transfer images prepared employing 2,6-dimethyl-p-aminophenol and 2,3-dimethyl-6-methoxy-p-aminophehol, respectively,

,as the silver halide developing agent, and are set forth for the purpose of providing comparative data; and

FIG. 4 is a graph showing corresponding rate curves of negative development versus transfer image formation determined by plotting reflection density as a function of time, wherein curves A and A represent the rate curves of negative development and transfer image formation, respectively, in accordance with the present invention and employing 2,3,6-trimethyl-p-aminophenol, as the silver halide developing agent, and curves B and B and C and C are corresponding rate curves employing Amidol and toluhydroquinone, respectively, and are set forth for the purpose of providing comparative data.

It has now been found that 2,3,5-trimethyl-p-aminophenol and, preferably, 2,3,6-trimethyl-p-amiriophenol silver halide developing agents, when employed in diffusion transfer processes, provide high speed transfer prints of exceptional quality, particularly alone, and also in combination with other silver halide developers such as ascorbic acid or hydroquinone or one of its derivatives.

In particular, 2,3,6-trimethyl-p-aminophenol and to a slightly lesser extent, 2,3,5-trimethyl-p-aminophenol have unexpectedly been found to provide an extensive Dynamic Range to silver diffusion transfer processes and to provide silver transfer prints of unexpectedly superior acuity.

As will be recognized, and as employed herein, the Dynamic Range of a diffusion transfer image comprises an empirically derived relative measurement of the range of exposure from which a useful transfer image may be derived. This range is determined by subtracting the log exposure value determined at the point on the toe portion of the transfer images characteristic curve, described hereinafter, where the slope is 0.4 from the log exposure value determined at the point on the shoulder portion of the curve, where the slope is 0.4. The resultant gradient range is then equivalent to the log of the ratio of the 0.4 toe gradient to the 0.4 shoulder gradient in units of exposure. The anti-log of the resultant exposure gradient provides the ratio of minimum to maximum exposure in a subject which can be usefully recorded by the film and is designated as the Dynamic Range.

In addition to providing the aforementioned unobviously high Diffusion Transfer Exposure Indices when employed as the sole developing agent, the stated paraarninophenols have also been found to be unique in possessing the property of providing an extremely low amount of induced or developer fog formation during the period of photographic development, of a photoexposed gelatino silver halide emulsion, necessary to provide for transfer image formation and, as a result, increased availability of undeveloped silver halide for transfer, as a function of the point-to-point degree of emulsion exposure, both in absolute quantities and in accordance with emulsion exposure gradients.

2,3,S-trimethyl-p-aminophenol may be prepared by coupling diazotized sulfanilic acid into 2,3,5-trimethylphenol and reducing the resultant 4-sulfophenylazo-2,3,5-' trimethyl-phenol. I

2,3,6-trimethyl-p-aminophenol may be prepared by oxidizing 2,3,5-trimethyl-p-aminophenol, forming the oxime of the resultant 2,3,S-trimethyl-p-quinone, and reducing the resultant 2,3,5-trimethyl-4-quinone-l-oxime.

Alternatively, 2,3,6-trimethyl-p-aminophenol may be prepared by coupling diazotized sulfanilic acid into 2,3,6- trimethyl-phenol and reducing the resultant 4-sulfophenylazo2,3,6-trimethyl-phenol.

It will be recognized that the developing agents of the present invention may be employed in the form of their acid addition salts, such as the hydrochloride, Where desired, and that the amino group may be substituted, for example, by a lower alkyl group such as a methyl group.

In particular, the silver halide developing agents of the present invention are highly useful in so-called high speed diffusion transfer processes wherein high quality silver transfer prints are obtained from a silver halide emulsion which has been substantially underexposed in relation to its A.S.A. rating. Such an exposure provides a latent image having a density gradient confined to the density in said negative.

low exposure or toe region of the negative materials characteristic curve.

The speed of a photosensitive material comprises generally an empirically derived relative measurement which may be defined as a value representing the reciprocal of the exposure required to produce a given result. Any precise definition of speed, therefore, is based upon the selection of a particular result as the standard reference point. A precise quantitative measure of speed has been developed from the Work of L. A. Jones et al., as reported in Mees, The Theory of the Photographic Process, the Macmillan Company, New York, 1944, Chapters XIX and XXII. This work suggested a system in which negative sensitive materials are assigned a speed that is in terms of the exposure required to give a negative image from which a positive print of specified quality can be produced.

Based on this work, the American Standards Association, Incorporated, has established standards for rating sensitive materials for speed. Under such standards, emulsion speed is considered as a value inversely proportional to the minimum exposure which must be incident upon the negative material, from the scene element of minimum brightness in which detail is visible, in order that a print of excellent quality can be made from the resultant negative. These standards specify techniques for plotting the characteristic H & D curve of a negative material, that is, the curve relating the logarithm of the original exposure of the negative to The value of speed derived from the standard characteristic curve so deter-mined is specified as equal to the reciprocal of the exposure, E, on the characteristic curve at which the slope is 0.3 times the average slope for a log exposure range of 1.5 of Which E is the minimum exposure. The precise method for determining speed in this manner is described in detail in the publication of the American Standards Association, Incorporated, PH 2.5-1954, and titled American Standard Method for Determining Photographic Speed and Exposure Index.

The A.S.A. speed rating is to be distinguished from what is termed the A.S.A. Exposure Index, for use with exposure meters and calculators. The A.S.A. Exposure Index is determined by the formula: A.S.A. Exposure Index=A.S.A. Speed/4. The exposure index so ob-' tained indicates generally the correct exposure rating to which an A.S.A. calibrated exposure meter must be set in order that it give correct exposure data for producing pictures of satisfactory high quality.

The A.S.A. speed rating is to be further distinguished from What may be termed Diffusion Transfer Process Exposure Index. In such processes, the exposure index may be based on a curve relating original exposure of the negative to the density in the resultant positive. It has been found experimentally that the Diffusion Transfer Exposure Index of a silver transfer process may be determined by plotting a characteristic curve of the reflection density of the positive as a function of the log exposure of the negative, determining the exposure in meter-candle-seconds (mcs.) at the point on this curve corresponding to a density of 0.50, and dividing the constant, 4.0, by the exposure so determined. The exposure index so obtained indicates generally the correct exposure rating of a silver transfer process to which an exposure meter, calibrated to the A.S.A. Exposure Index, must be set in order that it give correct exposure data for producing transfer prints of satisfactory high quality, and is sometimes referred to as the equivalent A.S.A. exposure index.

Both the A.S.A. Exposure Index and the Diffusion Transfer Exposure Index can be judged or rated according to sensitomeric criteria with exposure, that is the luminance flux reaching a unit area of the photosensitive surface, being measured in mcs. The equivalence of the foregoing methods of determining rated A.S.A.

Exposure Indices and Diffusion Transfer Exposure Indices can be readily established by obtaining a standardized silver transfer positive and determining the illumination, by measuring with an exposure meter calibrated according to an A.S.A. standard which includes a computer in which has been entered the shutter duration and f-stop of the camera, found necessary to provide the standard transfer print.

In the subsequent discussion, the term A.S.A. Exposure Index is intended to signify the exposure index determined in accordance with the aforementioned American Standards Association specifications. The term Diffusion Transfer Exposure Index is intended to signify, in reference to diffusion transfer processes, or the materials used therein, the exposure index as determined in the aforementioned manner. Both designations, in one sense, serve the same purpose. The A.S.A. Exposure Index of the negative is based upon the exposure to which the negative must be subjected in order to obtain a good photograph of a predetermined subject by conventional processing, whereas the Diffusion Transfer Exposure Index is based upon the exposure to which a negative for use in a silver diffusion transfer process must be subjected in order to obtain a good positive by that process. Both, therefore, are direct guides to the exposure setting which must be made in a camera in order to obtain proper exposure. Nevertheless, the two definitions of exposure must be carefully distinguished from each other because, although the A.S.A. Exposure Index is related qualitatively to the production of a positive of high quality, it is a term which describes the character of a negative material. This negative material, nevertheless, may be employed, for example, in a silver diffusion transfer process of the present invention to effect a Diffusion Transfer Exposure Index vastly different from the ASA' Exposure Index of the negative material. In the novel diffusion transfer processes of the present invention, a positive print of satisfactory high quality is produced from a negative material subjected to exposures less, in some cases many times less, than recommended by its rated A.S.A. Exposure Index. Such an exposure provides a latent image having a density gradient confined to the loW exposure or toe region of the negative materials characteristic curve.

Referring now to the drawing, FIGURE 1 illustrates one assemblage and process of the present invention in the performance of a diffusion transfer process for the production of positive silver prints. As depicted in the drawing, an aqueous alkaline fluid layer 12 of a silver halide developing agent chosen in accordance with the present invention and a suitable silver halide solvent are spread between photosensitive emulsion layer 11 which is superposed on support and image-receiving layer 13 which is atfixed to support layer 14. Image-receiving layer 13 preferably contains silver precipitating agents or nuclei such as the silver precipitating nuclei disclosed in U.S. Patent No. 2,698,237. Support layer 14 may comprise an opaque material where a reflection print is desired or may comprise a transparent material where a transparency is desired.

Fluid layer 12 may be obtained by distribution of the processing composition in a substantially uniform manner between photosensitive emulsion layer 11 and imagereceiving layer 13, forexample, in accordance with the procedures disclosed in US. Patent No. 2,543,181. For example, one or more rupturable containers may be attached to either photosensitive emulsion layer 11 and/ or image-receiving layer 13 such that upon super-position of the respective layers 11 and 13 said container or containers are so positioned as to be capable, upon rupture, of releasing their contents in a substantially uniform layer between and in contact with the opposed surface of each of said layers. Rupture of the container or containers and spreading of the contents thereof may be accomplished, for example, by compression between a pair of opposed, suitably gapped, rollers.

For clarity, the developing agent, the degree to which the photosensitive layer is exposed, and the character of the silver-receptive layer will be described in detail hereinafter.

The processing composition prefer-ably comprises a film-forming transfer processing composition. It may comprise, for example, one or more of the developing agents in accordance with the present invention, an alkali such as sodium hydroxide, a silver halide complexing agent such as sodium thiosulfate, and a high molecular weight film-forming thickening agent such as sodium carboxymethyl cellulose. All these materials are preferably in aqueous solution. These photographic agents are preferably contained in solution in the processing composition prior to the spreading thereof as layer 12, but they may be in part or in whole added to the processing composition as it is spread between the photosensitive emulsion 11 and image-receiving layer 13, said agents being so located on, in, or adjacent to a surface of one or both of said layers as to be dissolved by or otherwise interacted with the liquid agent when the latter wets said layers.

In carrying out the aforementioned transfer process, the photo-sensitive emulsion 11 is exposed to a predetermined subject matter to form therein a latent image of said subject matter. The exposed emulsion is superposed on image-receiving layer 13 and the photographic processing composition 12 spread between the opposed surfaces of said emulsion 11 and said image-receiving layer 13. Reagents permeate into the photo-sensitive emulsion 11, developing the latent image contained therein and forming a soluble silver complex of unexposed silver halide. Soluble silver complex 'is transported from photosensitive emulsion layer 11, at least in part, by imbibition, to print-receiving stratum 13 and the silver of the complex is precipitated thereon and/or therein to provide the desired positive image formation. The laminate formed by the spreading of the processing composition as layer 12 between photosensitive emulsion layer 11 and print-receiving layer 13 is kept intact for approximately 10 seconds to 1 /2 minutes, preferably 10 seconds, and at the termination of this time interval the printreceiving layer 13 is dissociated from photosensitive emulsion 11 as, for example, by manual stripping.

A further transfer process of the present invention for the production of positive silver prints is illustrated in FIG. 2 and comprises a spreader sheet 15, a layer of relatively viscous processing composition 12, a photosensitive emulsion layer 11 superposed on image-receiving layer 13 which is, in turn, superposed on a support layer 14. As stated in connection with the description of FIG- URE 1, image-receiving layer 13 preferably contains silver precipitating nuclei and support layer 14 maycomprise either an opaque or transparent material.

Fluid composition layer 12 may be obtained by spreading a photographic processing composition, for example, in a manner disclosed in US. Patent No. 2,698,244. As disclosed in the aforementioned patent, the liquid processing composition may be disposed in a rupturable container so positioned in regard to the appropriate surface of photosensitive emulsion layer 11 that, upon compression by spreader sheet 15, a substantially uniform layer 12 of processing composition is distributed over the external surface of said photosensitive emulsion 11, with respect to image-receiving layer 13.

In carrying out the last-mentioned transfer process, the photosensitive emulsion 11 is exposed to a predetermined subject matter to form therein a latent image of said subject matter. A substantially uniform distribution of processing composition 12 is distributed on the external surface of said emulsion 11, as for example, according to the previously described procedure. Processing composition reagents permeate into photosensitive emulsion 12, developing the latent image contained therein according to the point-to-point degree of exposure thereof. Substantially contemporaneous with the development of the latent image, an imagewise distribution of soluble silver complex is formed from unexposed and undeveloped silver halide within said emulsion. At least part of said silver complex, solubilized, is transferred, by imbibition, to print-receiving stratum 13. The transferred silver complexes are reacted therein to provide a positive, reversed image of the latent image. Subsequent to formation of the positive image in image-receiving layer 13, dissociation of said layer from emulsion layer 11 may be effected.

Where desired, the image-receiving layer 13 may be dissociated from emulsion layer 11 by stripping the emulsion from the surface thereof. A conventional stripping layer may be provided to facilitate separation of emulsion layer 11 from image-receiving layer 13 subsequent to transfer processing. Sufiicient abrasion-resistant properties may be provided to image-receiving layer 13 as to alleviate any necessity of subsequently overcoating the external surface of said image-receiving layer 13 with a transparent abrasion-resistant water-soluble plastic to prevent subsequent laceration and resultant degradation of the positive image. Image-receiving layer 13 may also comprise sufficient integral dimensional stability as to alleviate the necessity of a separate support layer 14.

In the last-mentioned processes, spreading of the liquid processing composition on the external surface of photosensitive emulsion layer 11 is preferably eflfected by rupture of a suitably positioned frangible container and distribution of its processing composition contents by means of a converted cellulose acetate spreader sheet, that is, a cellulose acetate sheet the surface of which has been converted to cellulose. When employed, the converted cellulose acetate spreader sheet may exhibit an adhesive capacity for the processing composition in excess of the adhesive capacity exhibited by the photosensitive emulsion.

A means is thus provided for effecting dissociation of the processing composition from contact with the photosensitive emulsion, subsequent to image formation, by dissociating the spreader sheet from its proximate relationship to the external emulsion surface.

It will be apparent that the facility with which the photosensitive emulsion layer is dissociated from contact with the print-receiving layer may be increased by providing a conventional stripping layer interposed between said emulsion and said print-receiving layer. The stripping layer may be coated on the surface of the print-receiving element and a photosensitive emulsion thereafter coated on the external surface of said stripping layer.

While distribution of the processing composition in dif-.

fusion transfer processes has been described utilizing a frangible container, it will be apparent that said container provides a convenient means of distributing the liquid processing composition to permit the processing to be effected within-a suitable camera apparatus. The diffusion transfer processes of this invention may be otherwise elfected. For example, a photosensitive element, after exposing a suitable apparatus and while preventing further exposure thereafter to actinic radiation, may be removed from such apparatus and permeated with the liquid processing composition as, for example, by coating, spraying, flowing, etc., the composition on said photosensitive element or otherwise wetting said element with a composition, following which the permeated, exposed, photosensitive element, still without additional exposure to actinic radiation, is brought into contact with the image-receiving element for image formation in the manner heretofore described.

The rupturable containers may be constructed in accordance with the disclosures set forth in US. Patent No. 2,634,888. Containers of this type are generally con structed from a blank comprising a flexible, deformable, three-ply sheet material comprising, respectively, an outer layer of kraft paper, a layer of metal foil and an inner layer or liner of a thermoplastic resin. The container blank is folded upon itself such as to provide a fluidcontaining capity and a container exhibiting a sealed passage adjacent to an edgethereof which may be substantially uniformly unsealed throughout a predetermined length of the seal passage upon application of stress to the container. The passage may be formed by the utilization of differential adhesion.

As previously noted, the print-receiving stratum preferably contains silver precipitating agents or nuclei, whose presence during the transfer process has a desirable effect on the amount and character of the silver precipitated during positive print formation. Examples of such silver precipitating agents are the metallic sulfides and selenides, thiooxalates, and thioacetamides, and colloidal metals disclosed in US. Patent No. 2,698,237. It is also desirable, as disclosed in that patent, to provide, as the vehicle for the silver precipitating agents, a macroscopically continuous film that consists of submacroscopic agglomerates of minute particles of a suitable water-insoluble, inorganic, preferably siliceous, material such as silica aerogel. The

, use of such a vehicle for the precipitating agents tends to cosity of from 1000 to 200,000 centipoises at a temperature of 20 C. in order to permit the solution to be readily controlled during and after spreading.

It will be apparent that the relative proportions of the agents of the developer composition set forth herein may,

be altered to suit the requirements of the operator. Thus, it is within the scope of this invention to modify the herein described developing compositions by the substitution of preservatives, alkalies, silver halides solvents, etc., other than those specifically mentioned. When desirable, it is also contemplated to include, in the developing composition, components such as restrainers, accelerators, etc. Similarly, the concentration of developing agent may be varied over a wide range and when desirable the developing agent may be disposed in the photosensitive element prior to the exposure of the emulsion. The developing agent may be disposed in a separate permeable layer of the photosensitive element and/or in the photosensitive emulsion.

The preferred pH of the developing agent containing solution is generally in excess of 12, for the most favorable results. The concentration of developer preferably ranges from about 1 to 8% and that of-the solvent from 0.3

' to 20%, by weight.

The emulsion support layer designated in the drawing as 10 may comprise any of the various types .of conventional rigid or flexible supports, for example, glass, paper, metal, and polymeric films of both the synthetic types and those derived from naturally occurring products.

The photosensitive emulsion stratum may comprise a commercially available silver halide gelatin emulsion such as sold by Eastman Kodak Company under the trade names Microfile, Spectrum Analysis, Contrast Process, S X X Aero Recon, Verichrome, Royal Pan,

Royal X Pan, or Tri X Pan, or sold by E. I. du Pont under the trade names Fine Grain Pan, High Speed Pan, Arrow Pan, or Superior 3, or sold by Ansco under the trade name Triple S Pan, or sold by Gevaert under the trade name Gevapan.

As previously stated, the silver halide developing agents of the present invention may also be used in small quantities with other silver halide developing agents, for example, hydroquinone or one of its derivatives, to produce high speed prints of exceptional quality by ditfusion transfer processes.

The present invention will be illustrated in greater detail in conjunction with the following specific examples which set out representative preparation of and employment of the silver halide developing agents of this invention in high speed diffusion transfer processes, which however are not limited to the details therein set forth and are intended to be illustrative only.

Example 1 2,3,5-trimethyl-p-aminophenol was prepared by dissolving 15.5 grams of .sulfanilic acid and 5.9 grams of sodium hydroxide in 160 cc. of water. The sulfanilic acid was then diazotized by the addition of 5.6 grams of sodium nitrate and a solution containing 25.1 cc. of 12 N hydrochloric acid in 25.1 cc. of water at to 4 C.

The diazo slurry was then added to a solution containing 11.0 grams of 2,3,5-trimethyl-phenol, 13.4 grams of sodium hydroxide and 80 cc. of water at C.

The resultant 4-sulfophenylazo-2,3,S-trimethyl-phenol was reduced by warming the solution to 40 C. and adding 74.3 grams of sodium hydrosulfite. The product, 2,3,5- trimethyl-p-aminophenol was separated from the mixture by filtration and washed with cold, deaerated water.

Example 2 2,3,6-trimethyl-p-aminophenol was prepared by dissolving the product of Example 1 in 150 cc. of hot 5% hydrochloric acid, adding 0.25 gram of stannous chloride to the solution and heating the mixture for minutes. Charcoal was then added, heating continued for 15 additional minutes, and the mixture filtered through a celite pad.

140 grams of hydrated ferric sulfate in cc. of water Was then added to the red filtrate and the mixture subjected to steam distillation.

The substantially colorless distillate, 2,3,5-trimethyl-pquinone, was heated to C. with stirring, and approximately cc. of alcohol was added. To the resultant homogenous solution were added 5.0 grams of hydroxylamine hydrochloride and the mixture heated until the odor of quinone was no longer detectable. Water was precipitate washed with cold, deaeraed water.

Under nitrogen,- 5.9 grams of the crystals were added to a solution containing 5.9 grams of sodium hydroxide dissolved in 85 cc. of water and maintained at a temperature below 40 C. 14.8 grams of sodium hydrosulfite were added to the solution and stirred for one hour. The resultant mixture was filtered under nitrogen and the The washed precipitate was then dissolved in 28.5 cc of 5% hydrochloric acid, charcoal added, and the mixture filtered through a celite pad. 12 .N hydrochloric acid was then added to the filtrate until crystallization commenced and the filtrate let stand for approximately 12 hours. The product, 2,3,6-trimethyl paminophenol hydrochloride, colorless crystals decomposing at 290 C., was then separated by filtration, washed with cold 12 N hydrochloric acidzwater solution, in the absence of air, and dryed in vacuo.

Example 3 Water cc 8,289.0 Hydroxyethyl cellulose (high viscosity) grams" 366.0 Sodium sulfite do 260.0 Sodium hydroxide do 425.0 Sodium thiosulfate do 741.0 6-Nitrobenzimidazole do 10.8 2,3,6-Trimethyl-p-aminophenol hydrochloride do 270.0 Potassium iodide do 15.0

between the photoexposed emulsion and the image-receiving element in a thin layer aproximately 0.003 of an inch thick. After a specified imbibition period, the emulsion, together with the layer of processing composition, was stripped from the image-receiving element ofeach film unit to uncover positive prints, which exhibited the characteristics set forth in the following table:

Shoulder Diflusion Imbibition Period Maximum Minimum %V 0.4 Toe 04 Transfer Dynamic in Seconds Density Density Slope Gradient Gradient Epgsure Range then added to the cloud point and the mixture allowed to Example 4 crystallize for approximately 12 hours. The mixture was then cooled to 10 C., the yellow crystals, 2,3,5-trimetl1yl- 4-quinone-1-oxime, MP. 184 to 186 C., separated by filtration, and the crystals washed with a cold 1:1 alcoholzwater mixture.

The process of Example 3 was repeated except that the 2,3,6-trimethyl-p-aminophenol hydrochloride was replaced with 2,6-dimethyl-p-aminophenol hydrochloride. The positive transfer image exhibited the following characteristics:

' Shoulder Difinsion Imbibition Period Maximum Minimum %}4 0.4 Toe 0.4 Transfer Dynamic in Seconds Density Density Slope Gradient Gradient Eiltpgsure Range I ance with the instant disclosure.

1 1 Example 5 The process of Example 3 was repeated except that the 2,3,6-trimethyl-p-aminophenol hydrochloride was replaced with 2,3-dimethyl-6-methoxy-p-aminophenol hydrochlo- C diffusion transfer processes employing 2,3,6-trimethylp-aminophenol uniquely possess an initially rapid negative development rate coupled with an initially slow transfer image formation rate, which, in turn, is followed by an extremely rapid transfer image formation rate rela- The process of Example 3 was repeated except that the 2,3,6-trimethyl-p-aminophenol hydrochloride was replaced with 2,3,S-trimethyl-p-aminophenol hydrochloride. The positive transfer image exhibited the following characterride. The positive transfer image exhibited the follow- 5 five to the r afv d l t t g characteristics: 1 CO fSPO1 111g neg 1 CV6 opmen ra C.

' Shoulder Diffusion Imbibition Period Maximum Minimum 0.4 Toe 0.4 Transfer Dynamic in Seconds Density Density Slope Gradient Gradient Eilrpgsure Range n ex ' l 1.24 a 0.22 0.48 i 2.80 i 1.20 840 40 Example 6 15 This initially rapid negative development coupled with an initially relatively slow transfer image formation facilitates development of, and discernment of, the low exposure level gradients within the exposure range, and thus facilitates accurate control of silver halide complex FIG. 3 shows characteristic curves of transfer images prepared in Examples -3, 4, and .6, wherein Curve A represents the characteristic curve of the transfer image of Example 3, employing an imbibit-ion period of sec onds, and Curves C, D and B represent the characteristic curves of the transfer images of Examples 4, 5 and 6, respectively.

It will be noted that the difference in dynamic ranges, the characteristic curve shapes and maximum transfer densities of the respective transfer images are so dramatic that there exists no question of subtlety in the clear superiority of the transfer images prepared in accord- In addition, the advantageous fact that the contrasts of the transfer images, prepared according to the instant procedure, are substantially constant, irrespective of the processing interval employed, over the image shown, is apparent from the table set forth in Example 3.

The instant processes provide the first known instance of a uniquely balanced relatively high speed, high maximum density, low minimumdensity and high dynamic range diffusion transfer system. While .processes may be set forth which will achieve one or more of these properties, invariably such has been accomplished at the expense of the remaining properties. Never previously has such a desirable balance of properties been achieved on this scale employing a plurality of agents, much less the single developing agents of theinstant disclosure. For example, in order to obtain high speed in the processes of the prior art, density and/or operational exposure latitudes'have hadto be sacrificed.

Specifically, for a given Diffusion Transfer Exposure Index, the employment of the instant developing agents intrinsically provides a greater dynamic range than that provided by other developing agents, for a given comparable transfer image quality, substantially irrespective of the gelatino silver halide emulsion employed, its conven tional A.S.A. rating, and/ or the various and sundry conventional adjuncts commonly incorporated in the processing composition.

FIG. 4 sets forth rate curves of both negative development and positive transfer image formation of transfer film units processed in accordance with Example 3 and employing 2,3,6-trimethyl-p-aminophenol, Amidol and toluhydroquinone, respectively.

As will be observed from mutual comparison of negative curves A, B and C, and positive curves A B and istics' formation and transfer, during the initial stages of proc- Shoulder Diffusion Imbibition Period Maximum Minimum 0.4 Toe 04 Transfer Dynamic in Seconds Density Density Slope Gradient Gradient Exposure Range Index essing by, in part, reducing premature and indiscriminate complex formation and transfer, prior to control by development of-photoexposed silver halide.

The following relatively rapid transfer image formation rate relative to the then decreasing negative development rate then provides transfer image formation at a rate greatly exceeding the formation of fog in the negative and thus facilitates the total acuity of transfer image formation.

The chief function of a photographic negative material as used in pictorial photography is to reproduce, as density differences, the luminance differences existing 'in the object photographed. The minimum useful exposure will, therefore, be that required to reproduce the minimum difference existing in the shadow regions of the object by means of some minimum density difference in the resulting image.

'When the developing agents designated are employed in high speed diffusion transfer processes, the region of the A.S.A. characteristic curve of the negative used in accordance with the present invention lies at a relatively low exposure level and corresponds to an exposure gradient predominantly below approximately 0.015 mcs.

It has been determined that, under the proper conditions, the activity of the silver halide developing agent, in accordance with the present invention, is concentrated in the extreme outer layer of the silver halide stratum. This phenomenon is probably due to the fact that the activity of the developer is so rapid that oxidation of the developer occurs before it is able to penetrate very deeply into the silver halide stratum. In comparison, the silver halide developing agent 'of conventional silver diffusion transfer processes is active in deeper layers of the silver halide stratum.

As illustrated in the aforementioned specific examples the photosensitive emulsions of the present processes are underexposed in relation to their respective A.S.A. Exposure Index to produce therein a weak latent image having an exposure gradient predominantly in the toe region of the A.S.A. density versus log exposure curve of the photosensitive emulsion. The emulsion is therefore exposed to produce a latent image lying in the toe region of the A.S.A. characteristic curve for the negative emulsion such that, by the standard A.S.A. development method, it would be impractical to develop the emulsion such as to provide a useful conventional negative image. By means of the compositions, products and processes of photosensitive emulsion having'a stated A.S.A Exposure Index and provide said emulsion with an effective exposure that ordinarily would require a photosensitive emulsion having a higher A.S.A. Exposure Index to provide an acceptable positive print resultant therefrom.

With conventional developing practices, good negatives can be obtained only from an emulsion that has been sufiiciently exposed within the range of exposures specified for the emulsion. Underexposed emulsions result in a negative having only an image from which it is impractical to obtain a satisfactory print by conventional processes.

The present invention obviates the problem of constructing a satisfactory negative from an underexposed emulsion, for example, by intensification, hypersensitization, latensification techniques, so as to obtain a satisfactory positive print. In addition, the present invention provides satisfactory positive images from both underexposed and adequately exposed conventional silver halide photosensitive emulsions. As previously mentioned, a convenient measure of the amplification of image development, obtained according to the present disclosure, over the results obtained from conventional development practices, is in terms of increase in the speed or quantum excitation sensitivity of the emulsion as indicated by the results previously set forth, over the normal specified speed of the same emulsion as determined by the results of standard development practice.

It will be recognized that the steps of the instant processes may, where desired, be combined with such conventional speed-increasing steps as the aforementioned hypersensitization, latensification, etc.

Since certain changes may be made in the above products, processes and compositions without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The photographic process which comprises the steps of exposing a photosensitive gelatino silver halide emulsion with a light flux incident thereon not substantially in excess of the exposure range delineated by the toe region of said emulsions characteristic H and D curve, determined according to A.S.A. Standard PH 2.5-1954; developing exposed silver halide in said photosensitive emulsion with an aqueous alkaline solution of a compound selected from the group consisting of 2,3,5-trimethyl-p-aminophenol and 2,3,6-trimethyl-p-aminophen01; contacting undeveloped silver halide with a silver halide solvent and forming thereby an imagewise distribution of a soluble silver complex in the unexposed areas of said emulsion; transferring from said emulsion, at least in part, said imagewise distribution of soluble silver complex to a print-receiving layer, containing a silver precipitating agent, in superposed relationship to said emulsion; and precipitating said silver complex to provide thereby a reversed, positive print exhibiting a full pictorial density range.

2. A photographic process of claim 1 including the step of separating said print-receiving layer from its superposed relationship with said photosensitive emulsion at some stage subsequent to positive print formation.

3. The photographic process of claim 1 wherein said solution has a pH in excess of about 12.

4. The photographic process which comprises the steps of selectively exposing a photosensitive gelatino silver halide emulsion with an illuminance flux incident thereon predominantly below 0.015 meter-candle-seconds; developing exposed silver halide in said photosensitive emulsion with an aqueous alkaline solution containing a silver halide developing agent selected from the group consisting of 2,3,S-trimethyl-p-aminophenol and 2,3,6-

trimethyl-p-aminophenol and a silver halide solvent; substantially contemporaneous with said development, contacting unexposed and undeveloped silver halide therein with said silver halide solvent and forming thereby an imagewise distribution of a soluble silver complex in the unexposed areas of said emulsion,,as a function of the point-to-point degree of exposure thereof; transferring from said emulsion, at least in part, by imbibition, said imagewise distribution of soluble silver complex to a print-receiving layer, containing silver precipitating nuclei, in superposed relationship to said emulsion; and there precipitating silver complex to provide thereby a reversed, positive full scale silver print of said latent image.

5. The photographic process which comprises the steps of exposing a photosensitive gelatino silver halide emulsion with a light flux incident thereon not substantially in excess of the exposure range delineated by the toe region of said emuls'ions characteristic H and D curve, determined according to A.S.A. Standard PH 2.5-1954; developing exposed silver halide in said photosensitive emulsion with an aqueous solution of a silver halide developing agent selected from the group consisting of 2,3,5-trimethyl-p-aminophenol and 2,3,6-trimthyl-p aminophenol; contacting undeveloped silver halide with a silver halide solvent and forming thereby an imagewise distribution of soluble silver complex in the unexposed areas of said emulsion; transferring from said emulsion. at least in part, said imagewise distribution of soluble silver complex to a print-receiving element, containing silver precipitating agents, in superposed relationship to said emulsion; and precipitating said silver complex to provide thereby a reversed, positive print possessing a characteristic curve with a slope greater than the slope of said H and D curve, said .positives characteristic curve determined by plotting the reflection density of the positive print as a function of the log exposure of the negative.

6. A photographic product which comprises a plurality of layers including a support layer, a gelatino silver halide emulsion layer on one side of said support layer, and a layer containing a silver halide developing agent selected from the group consisting of 2,3,5-trimethyl-paminophenol and 2,3,6-trimethyl-p-aminophenol on the same side of said support layer.

7. A photographic product as defined in claim 6 wherein said silver halide developing agent is in said emulsion layer.

8. A photographic composition which comprises an aqueous alkaline solution of a silver halide solvent and a silver halide developing agent selected from the group consisting of 2,3,S-trimethyl-p-aminophenol and 2,3,6- trimethyl-p-aminophenol.

9. A process of developing a photoexposed silver halide emulsion which comprises contacting said emulsion with an aqueous alkaline solution of a silver halide develop ing agent selected from the group consisting of 2,3,5- trimethyl-p-aminophenol and 2,3,6-trirnethyl-p-aminophenol.

10. A process as defined in claim 9 wherein said solution contains a silver halide solvent and said emulsion is disposed in contiguous relationship to a diffusion transfer print-receiving layer retaining silver precipitating agents during said contact.

11. A process as defined in claim 9 wherein said developing agent is 2,3,6-trimethyl-p-aminophenol.

12. A process as defined in claim 10 wherein said developing agent is 2,3,S-trimethyl-p-aminophenol.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

J. T. BROWN, Assistant Examiner. 

1. THE PHOTOGRAPHIC PROCESS WHICH COMPRISES THE STEPS OF EXPOSING A PHOTOSENSITIVE GELATINO SILVER HALIDE EMULSION WITH A LIGHT FLUX INCIDENT THEREON NOT SUBSTANTIALLY IN EXCESS OF THE EXPOSURE RANGE DELINEATED BY THE TOE REGION OF SAID EMULSION''S CHARACTERISTIC H AND D CURVE, DETERMINED ACCORDING TO A.S.A. STANDARD PH 2.5-1954; DEVELOPING EXPOSED SILVER HALIDE IN SAID PHOTOSENSITIVE EMULSION WITH AN AQUEOUS ALKALINE SOLUTION OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF 2,3,5-TRIMETHYL-P-AMINOPHENOL AND 2,3,6-TRIMETHYL-P-AMINOPHENOL; CONTACTING UNDEVELOPED SILVERR HALIDE WITH A SILVER HALIDE SOLVENT AND FORMING THEREBY AN IMAGEWISE DISTRIBUTION OF A SOLUBLE SILVER COMPLEX IN THE UNEXPOSED AREAS OF SAID EMULSION; TRANSFERRING FROM SAID EMULSION, AT LEAST IN PART, SAID IMAGEWISE DISTRIBUTION OF SOLUBLE SILVER COMPLEX TO A PRINT-RECEIVING LAYER, CONTAININING A SILVER PREICIPITATING AGENT, IN SUPERPOSED RELATIONSHIP TO SAID EMULSION; AND PRECIPITATING SAID SILVER COMPLEX TO PROVIDE THEREBY A REVERSED, POSITIVE PRINT EXHIBITING A FULL PICTORIAL DENSITY RANGE. 